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Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids

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On Tue, Nov 3, 2015 at 10:58 PM, Willy Tarreau <w@1wt.eu> wrote:
> On Tue, Nov 03, 2015 at 03:29:55PM -0800, Kees Cook wrote:
>> Using "write" does kill the set-gid bit. I haven't looked at
>> why.
>> Al or anyone else, is there a meaningful distinction here?
>
> I remember this one, I got caught once while trying to put a shell into
> a suid-writable file to get some privileges someone forgot to offer me :-)
>
> It's done by should_remove_suid() which is called upon write() and truncate().
>
>> Should the
>> mmap MAP_SHARED-write trigger the loss of the set-gid bit too? While
>> holding the file open with either open or mmap, I get a Text-in-use
>> error, so I would kind of expect the same behavior between either
>> close() and munmap(). I wonder if this is a bug, and if so, then your
>> link patch is indeed useful again. :)
>
> I don't see how this could be done with mmap(). Maybe we have a way to know
> when the first write is performed via this path, I have no idea.

do_wp_page might be a decent bet.

--Andy
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Re: [PATCH] namei: permit linking with CAP_FOWNER in userns Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> - 2015-11-02 16:20 +0100
  Re: [PATCH] namei: permit linking with CAP_FOWNER in userns Serge Hallyn <serge.hallyn@ubuntu.com> - 2015-11-02 19:10 +0100
    Re: [PATCH] namei: permit linking with CAP_FOWNER in userns Andy Lutomirski <luto@amacapital.net> - 2015-11-02 21:00 +0100
      [RFC] namei: prevent sgid-hardlinks for unmapped gids Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> - 2015-11-03 01:50 +0100
        Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Serge Hallyn <serge.hallyn@ubuntu.com> - 2015-11-03 16:50 +0100
        Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-03 19:30 +0100
          Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> - 2015-11-04 00:30 +0100
            Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-04 00:40 +0100
              Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Willy Tarreau <w@1wt.eu> - 2015-11-04 08:00 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-04 19:10 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-04 19:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Willy Tarreau <w@1wt.eu> - 2015-11-04 19:30 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Willy Tarreau <w@1wt.eu> - 2015-11-04 19:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-06 23:00 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-06 23:40 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-07 01:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-07 01:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-07 01:50 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-07 06:10 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Theodore Ts'o <tytso@mit.edu> - 2015-11-08 03:10 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Jan Kara <jack@suse.cz> - 2015-11-10 16:10 +0100
          Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids "Serge E. Hallyn" <serge@hallyn.com> - 2015-11-04 15:50 +0100

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